Level 3 Communications Inc., an Internet backbone company that supports Netflix Inc.’s increasingly popular movie streaming service, complained Monday that cable giant Comcast Corp. is charging it an unfair fee for the right to send data to its subscribers.

Comcast replied it is being swamped by a flood of data and needs to be paid.

Level 3 said it agreed to pay under protest, but that the fee violates the principles of an “open Internet.” It also goes against the Federal Communications Commission’s proposed rules preventing broadband Internet providers from favoring certain types of traffic, it said.

“Comcast is effectively putting up a toll booth at the borders of its broadband Internet access network, enabling it to unilaterally decide how much to charge for content,” said Level 3’s chief legal officer, Thomas Stortz, in a statement.

Comcast called Level 3’s position “duplicitous” and said a previous deal for the companies to handle traffic for each other had become unbalanced in Level 3’s favor.